The present invention relates generally to the removal of ceramic casting cores from a cast component. More particularly, the present invention relates to a closed leaching system that varies the pressure within the system to change the temperature of the leaching fluid during removal of the ceramic material from the cast component. Although the present invention was developed for manufacturing gas turbine engine components, many additional applications of the present invention are outside of this field.
Typically in the design of gas turbine engine components there is included internal cavities, openings and/or passages for the flow of cooling media. Generally, the internal cavities, openings and/or passages are formed by the placement of a ceramic core into the mold and molten metal is then solidified within the mold and around the core to form the casting. The ceramic core must then be removed from the casting to yield the desired cast component. The scientific community analyzing the removal of ceramic cores from castings appreciates that the process should be benign to the material used to form the casting.
There are prior processes for leaching ceramic material from the interior of cast metallic components. One prior process for leaching ceramic material from cast metallic components is set forth in U.S. Pat. No. 5,332,023 to Mills, which is incorporated herein by reference. Within the ""023 patent there is disclosed a leaching system wherein the pressure within an enclosure is varied between atmospheric pressure and no more than 0.45 bar below atmospheric pressure to induce intermittent boiling. The intermittent boiling agitates the leaching fluid and causes a mixing of the leaching material. Included in this disclosed leaching system is that there is a connection to atmospheric pressure that is controlled to increase the pressure within the enclosure on demand and a vacuum pump that is used to lower the pressure within the enclosure on demand. Accordingly, each time the pressure is changed within the enclosure a quantity of the molecules within the enclosure is changed. This change in quantity and/or type of molecules causes a change in the concentration of the leaching material. A limitation associated with the system disclosed in the ""023 patent is that the change in concentration of the leaching material affects many parameters including, but not limited to, boiling point, leaching efficiency and the potential for chemical degradation of the cast component
Although many of the prior processes for leaching ceramic material from the interior of cast metallic components are steps in the right direction, there still remains a need for additional improvement. The present invention satisfies this need in a novel and non-obvious way.
One form of the present invention contemplates a method for removing a ceramic material from a cast component. The method, comprising: (a) placing the cast component within a vessel with at least a portion of the ceramic core in contact with a leaching material; (b) heating the leaching material; (c) reducing the pressure within the vessel to superheat the leaching material and nucleate boiling bubbles on at least the cast component; (d) increasing the pressure within the vessel to raise the boiling temperature of the leaching material; and (e) wherein during at least (c) and (d) the vessel is closed to inhibit a change in the concentration of the leaching material by evaporation from the vessel.
Another form of the present invention contemplates a system using leaching material to remove material from an object. The system, comprising: a vessel adapted to contain a quantity of the leaching material, the vessel defines a closed volume including a headspace for gaseous material; a heater operable to heat the leaching material within the vessel; a sensor for sensing a first parameter associated with the leaching material within the vessel; and, a volume variation mechanism defining a portion of the closed volume, the volume variation mechanism operable to change the size of the headspace and pressure therein without changing the number of atoms within the closed volume, the volume variation mechanism being operable upon the first parameter satisfying a predetermined condition.
Another form of the present invention contemplates a system for removing ceramic material from a molded metallic object. The system, comprising: a closed vessel having an interior volume containing a first portion for leaching material and a second portion for gaseous material; a heat supply for heating the leaching material within the vessel; a condenser coupled with the vessel for condensing vapor within the vessel; a sensor for sensing a parameter of the leaching material; means for precisely changing the pressure within the closed vessel without changing the quantity of atoms within the interior volume; and, an electronic controller for operating the means for precisely changing the pressure according to time and feedback from the sensor.
One object of the present invention is to provide a unique method for removing ceramic material from cast components.
Related objects and advantage of the present invention will be apparent from the following description.